Communication networks come in a variety of forms. Notable networks include wireline and wireless. Wireline networks include local area networks (LANs), digital subscriber line (DSL) networks, and cable networks, among others. Wireless networks include cellular telephone networks, classic land mobile radio networks and satellite transmission networks, among others. These wireless networks are typically characterized as wide area networks. More recently, wireless local area networks and wireless home networks have been proposed, and standards, such as Bluetooth and IEEE 802.11, have been introduced to govern the development of wireless equipment for such localized networks.
A wireless local area network (WLAN) typically uses infrared (IR) or radio frequency (RF) communications channels to communicate between portable or mobile computer terminals and stationary access points or base stations. These access points are, in turn, connected by a wired or wireless communications channel to a network infrastructure which connects groups of access points together to form the LAN, including, optionally, one or more host computer systems.
Wireless protocols such as Bluetooth and IEEE 802.11 support the logical interconnections of such portable roaming terminals having a variety of types of communication capabilities to host computers. The logical interconnections are based upon an infrastructure in which at least some of the terminals are capable of communicating with at least two of the access points when located within a predetermined range, each terminal being normally associated, and in communication, with a single one of the access points. Based on the overall spatial layout, response time, and loading requirements of the network, different networking schemes and communication protocols have been designed so as to most efficiently regulate the communications.
IEEE Standard 802.11 (“802.11”) is set out in “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” and is available from the IEEE Standards Department, Piscataway, N.J. IEEE 802.11 permits either IR or RF communications at 1 Mbps, 2 Mbps and higher data rates, a medium access technique similar to carrier sense multiple access/collision avoidance (CSMA/CA), a power-save mode for battery-operated mobile stations, seamless roaming in a full cellular network, high throughput operation, diverse antenna systems designed to eliminate “dead spots,” and an easy interface to existing network infrastructures.
The 802.11a standard defines data rates of 6, 12, 18, 24, 36 and 54 Mbps in the 5 GHz band. Demand for higher data rates may result in the need for devices that can communicate with each other at the higher rates, yet co-exist in the same WLAN environment or area without significant interference or interruption from each other, regardless of whether the higher data rate devices can communicate with the 802.11a devices. It may further be desired that high data rate devices be able to communicate with the 802.11a devices, such as at any of the standard 802.11a rates.
One challenge in designing a wireless transmission system involves transmit beamforming using an antenna array. Beamforming focuses signals toward a receiver in such a way that they combine at the receiver resulting in a stronger signal. If signals are transmitted off multiple antennas and focused toward a designated receiver rather than being transmitted in an omni-directional fashion, the composite phase and amplitude of the transmission determines the effectiveness of the beam-forming. The phase and amplitude relationship between the transmit antennas is adjusted to focus this energy at the intended receiver. One way to adjust a beam-forming transmitter is to incorporate additional circuitry on the radio. The circuitry is used to compute and share the conditions observed by the receiver. The transmitter then performs a complex calculation to adjust the beamforming antenna array. However, this solution can be expensive.
Increasing the effective signal strength and/or receiver sensitivity enables more efficient communications. Increased signal strength may enable service providers to more effectively use their equipment. Consumers may realize a cost savings as well.